Gas distributors for fluidized beds

ABSTRACT

A fluidized bed gas distributor is disclosed, wherein the gas distributor allows the fluidized bed to operate with intermittant fluidization, with substantial elimination of natural backflow of fluidized particles. The gas distributor comprises a pair of horizontal pipes disposed within one another, having an annular space thereinbetween. Holes are located in the inner pipe and the outer pipe for the passage of gas therethrough. The holes in the outer pipe are located in the lowermost one-third of the circumference of the pipe and are staggered in a circumferential and/or longitudinal direction relative to the holes in the inner pipe.

ilnited States Patent 1191 Evans Feb. 19, 1974 [54] GAS DISTRIBUTORS FOR FLUIDIZED BEDS 1,729,149 9/1929 Brown et al. 239/558 3,347,473 10/1967 Steck 239/560 [75] Inventor- Bruce Ronald P 3,599,877 8/1971 Goldschmied 239/562 Lambton, Australia [73] Assignee: The Broken Hill Proprietary Primary Examiner-Lloyd L. King Company Limited, Melbourne, Attorney, Agent, or FirmCushman, Darby & Victoria, Australia Cushman [22] Filed: Nov. 8, 1971 l [57] ABSTRACT [211 App 196578 A fluidized bed distributor is disclosed, wherein the gas distributor allows the fluidized bed to operate [30] Foreign Application Priority Data with interrnittant fluidization, with substantial elimina- Nov. 10, 1970 Australia 3152 70 tion of natural backflow 0f fluidized Particles The gas distributor comprises a pair of horizontal pipes dis- 52 US. Cl 239/553, 239/562, 239/567 Posed within one anetheri having an annular Space 51 Int. (:1 B05b 1/14 thereinbetween- Holes are located in the inner P p [58] Field of Search 239/566, 553, 560, 558, 567 and the Outer p p for the Passage of gas therethwugh- [56] References Cited UNITED STATES PATENTS 3,531,053 9/1970 Milleret al. 239/566 X 1,596,452 8/1926 Reeves et al 239/553 The holes in the outer pipe are located in the lowermost one-third of the circumference of the pipe and are staggered in a circumferential and/or longitudinal direction relative to the holes in the inner pipe.

13 Claims, 5 Drawing Figures 11 11a] Hb PAIENTED FEB I 91974 SHEET 2 [1F 2 1 GAS DISTRIBUTORS FOR F LUIDIZED BEDS This invention relates to gas distributors for fluidized bed apparatus and is particularly, although by no means exclusively, concerned with distributors for fluidizing beds of hot particulate material suitable for for the carbonization of green briquettes of coal immersed in the bed.

To be suitable for intermittent fluidization processes a gas distributor must be designed to prevent such backflow of the particulate material defining the bed as would choke and prevent operation of the distributor. An object of this invention is to provide a gas distributor for fluidized bed apparatus which operates satisfactorily to fluidize particulate material, while a more specific object is to preventundesirable backflow of bed material which would tend to block the gas distributor.

In this specification the term gas includes air or other fluidizing gas, or vapour such as steam or LPG.

According to the invention a gas distributor for fluidized bed apparatus is provided which comprises a pair of pipes disposed one within the other, a space between at least a substantial part of the adjacent surfaces of said pipes, holes in the inner pipe for admitting gas from the inner pipe to said space, and holes in the outer pipe for discharging gas from said space to the fluidized bed.

The pipes may be of cylindrical, polygonal or other suitable shape in cross-section, and are preferably cylindrical. Theinner pipe may be disposed concentrically or eccentrically within the outer pipe.

. The term holes in this specification includes apertures of circular, polygonal or any other suitable shape.

In order to minimise or prevent backflow of particulate material into the space between the pipes, the holes in the outer pipe are preferably arranged to face downwardly, i.e., are positioned in the lowermost onethird of the circumference of the outer pipe and are preferably above the lowermost portion of the said pipe by a circumferential distance not exceeding one-eighth of the circumference of the said pipe.

In order to enable the gas flow in the inner pipe to sweep particulate material out through the holes in the inner pipe, such holes are preferably positioned in the lowermost portion of the said pipe, and desirably are located in the lowermost one-third of its circumference.

Preferably, the holes in-the inner and outer pipes are spaced in a substantially regular pattern along the length of the pipes so that the flow of gas from the holes in the inner pipe to the holes in the outer pipe is substantially uniform along the length of the pipes.

In a preferred arrangement, the pipes are concentric and there is a single row of regularly spaced holes in the lowermost portion of the inner pipe, and two rows of regularly spaced holes in the outer pipe, one row on one side of the outer pipe and the other row on the other side of the outer pipe, each row being above the lowermost portion of the outer pipe by a circumferential distance equivalent to about one-eighth of the circumference of the outer pipe, there being at each longitudinal position midway between the holes in the inner pipe either a pair of holes or a single hole alternately on one side and then the other of the outer pipe.

However, the invention is not confined to the foregoing arrangements since other workable possibilities exist. For example, backflow into the space between the pipes during non-fluidization periods can be tolerated providing the gas flow during the next fluidization period can sweep material out of the space to an extent sufficient to allow the desired gas discharge through the holes in the outer pipe. Thus, the holes in the outer pipe can be arranged to face horizontally or even upwardly providing the gas flow from the holes in the lower portion of the inner pipe is strong enough to adequately clear the space between the pipes. Similarly, the holes in the inner pipe can be in positions higher than those preferred providing the amount of material that might accumulate inside the lower portion of the pipe does not interfere with satisfactory operation of the distribu- 1201.

A combination that should obviously be avoided is one having coincident holes in the uppermost portion of both pipes, which would enable a direct flow of particulate material into the inner pipe, and into the space, during non-fluidization periods. However, an arrangement in which there are holes in the uppermost portion of the outer pipe is workable providing these holes are not coincident with holes in the inner pipe, and especially if the distance between the adjacent surfaces of the pipes at this location is sufficiently small in relation to the hole size that the backflow of material is arrested by the formation of small heaps supported by the inner pipe.

In order to minimise the accumulation of material in the extreme ends of the space between the pipes, the end holes in the inner pipe are preferably located outwardly of the end holes in the outer pipe, i.e., there is one less longitudinal hole position in the outer pipe than there is in the inner pipe.

The inner and outer pipes may be spaced .apart and connected together by means of spacers secured to the inner pipe and arranged at circumferential and longitudinal intervals. Such spacers are not necessary if the pipes are relatively short.

The gas distributor preferably comprises a series of double pipes arranged horizontally in parallel relationship and spaced apart by a suitable distance. The pipes forming the gas distributor extend across the area of the fluidizing chamber, e.g., across the lower area or base thereof, and are connected to a source of fluidizing gas under pressure.

When intermittent gas supply is used, if any particulate material (e.g., sand) flows back into the space between the pipes it is blown back into the bed with the next fluidization cycle. Also any small particles in the gas supply are completely blown through the double pipe diffuser system.

In order to achieve substantially uniform flow of gas through the holes in the outer pipe, the pressure drop of the gas in flowing through the holes in the inner pipe is large compared with the pressure drop along the length of the inner pipe, and the pressure drop of the gas in flowing through the holes in the outer pipe is large compared with the pressure drop of the gas in flowing through the space between the pipes. v The fluidizing gas velocities in the inner pipe should be such as to achieve horizontal transport of suspended solids (e.g., sand) that may have back-filled into the pipes.

The gas distributor of this invention has the following advantages: I

1. No moving parts.

takes place, the system is self cleaning'when fluidizing medium again flows through the distributor into the fluidized bed. This fluid flow forces the particles back into the bed. I

5. The distributor can be made from pipe of any suitable cross-sectional configuration and from any suitable material depending on the service conditions, particularly temperature.

6. TI-Ie distributor operates satisfactorily up to high temperatures without buckling or warping. Buckling severely limits the operating conditions for existing perforated plate distributors.

7. The distributors are easier to manufacture and install than existing perforated plate or bubble cap type distributors. They can be installed at various levels in a fluidized bed for injecting different fluids; e.g., a lower row of double pipe distributors could supply air or oxygen and an upper row could supply gas for fluidized bed combustion. Alternatively, gases could be injected at various levels for chemical reactions to take place.

Reference will now be made to the preferred embodiments of the invention illustrated in the accompanying drawings, wherein:

'FIG. 1 is a view in sectional elevation, partly broken away, of a fluidized bed apparatus incorporating a gas distributor according to this invention,

.FIG. 2 is a view in sectional plan taken on the line .,2 -2 of FIG. 1.

FIG. 3 is a view in enlarged sectional elevation taken on the line 33 of FIG. 2,

FIG. 4 is a view in sectional elevation taken on the line 4-4 of FIG. 3, and

FIG. 5 is a viewin sectional elevation, similar to FIG. 4, showing a modified arrangement in which the inner pipe is disposed eccentrically within the-outer pipe.

Referring to the drawings, the reference numeral indicates a fluidizing chamber or vessel having vertical side walls 11 and a bottom wall or floor 12. The walls 11 and 12 comprise a refractory lining 11a, 12a and an outer metal casing 11b, 12b.

A series of double pipes 14 are arranged in parallel relationship in the lower part of the fluidized bed chamber 10, the said double pipes 14 being horizontal. The double pipes 14, which constitute the distribtuor for the fluidizing gas, may be located at any desired level in the fluidizing chamber 10 and if desired a plurality of gas distributors each comprising a series of double pipes 14 may be arranged at different levels in the fluidizing chamber 10.

Each double pipe, which is shown in greater detail in FIGS. 3 and 4, is arranged so that one end projects through an aperture in the wall 11 of the chamber 10, and the inner pipe of each double pipe 14 is connected externally of the chamber 10 to a source of fluidizing gas, such as air, under pressure.

Referring particularly to FIGS. 3 and 4, each double pipe 14 comprises an inner pipe 15 and an outer pipe 16, the inner pipe 15 being concentrically disposed within the outer pipe 16 in the form of the invention shown in FIGS. 1 to 4. The pipes are held in their relative positions by spacers 17 which are conveniently located at I20 apart and at intervals along the pipes 15, 16 and which are normally secured to the inner pipe 15.

The end of each double pipe 14 projects through an aperture 19 in the side wall 11 of the chamber 10 and the outer pipe 16 fits through a sleeve 20 having an outer flange 21 which engages the outer face of the casing 11b. The outer end 22 of the outer pipe 16 is externally threaded and an internally threaded bush 23 is screwed onto the end 22 of the outer pipe 16. An inner flange 24 on the bush 23 is secured to the flange 21 of the sleeve 20 by studs 25. A plug 26 is fitted over and welded to the projecting outer end of the inner pipe 15 and is screwed into the outer end of the bush 23, A flange 27 on the plug 26 abuts against the outer endof the bush 23. The inner ends of the pipes 15 and 16 within the chamber 10 are closed by plates 28b and 280 respectively.

By this arrangement'the inner pipe 15 and outer pipe 16 are held in their correct positions relative to one another, the said pipes are also held securely in position in the fluidization chamber 10, and the distributor may be readily dis-assembled when required.

The outer ends of the inner pipes 15 are connected to a source (not shown) of fluidizing gas under pressure.

Each inner pipe 15 is provided with a series of gas apertures 30 which are directed downwardly and are conveniently located along the lowermost edge of the pipe 15 at spaced intervals therealong.

Each outer pipe 16 is provided with a series of gas Outlet apertures 31, 32 which may be at any point on the periphery of the pipe 16 and are preferably arranged in pairs located at points spaced by about oneeighth of the circumference of the pipe 16 above the lowermost edge of said pipe, as shown in FIG. 4. The apertures 31, 32 in the pipe 16 are offset or staggered both circumferentially and longitudinally relative to the apertures 30 in the pipe 15. The apertures 30, 31, 32 may be of any suitable configuration and are preferably circular.

In operation, fluidizing gas under pressure is supplied to the outer ends of the innerpipes 15 and is caused to flow through the apertures 30 in each inner pipe into the annular space 33 between each inner pipe 15 and its outer pipe 16. The fluidizing gas then flows through said annular space 33 to the apertures 31, 32 in the outer pipe 16 and then outwardly through the apertures 31, 32 into the fluidization chamber 10 where it is distributed into and maintains the fluidized 'bed (not shown).

In the double pipe arrangement shown in FIG. 5, the inner pipe 15 is arranged eccentrically within the outer pipe 16 and the said pipes 15, 16 are in contact at their uppermost points, the maximum distance between the said pipes being at their lowermost points. The apertures 30 in the pipe 15 and the apertures 31, 32 in the pipe 16 are located similarly to the corresponding apertures in the double pipe arrangement shown in FIG. 4.

To obtain satisfactory gas distribution the flow of gas through the apertures 31, 32 along the pipes 16 should be substantially equal, and this may be achieved by ensuring that the pressure drops across the gas distributor are maintained as previously specified.

It is found that in the operation of the gas distributor of this invention, any backflow of the particulate fluidizing medium (such as sand) into the inner pipes is substantially prevented, and that any of such medium which may back-flow into the outer pipes 16, when the flow of gas is interrupted, is effectively removed therefrom when the gas supply is re-applied.

Gas distributors for fluidizing a given bed using a given gas may be designed by the following procedure, which makes use of known technology:

a. the required fluidizing gas flow rate in m /h per 1m of bed is determined experimentally or by calculation;

. a reasonable spacing for, and hence the number of, gas distributors, is selected from known fluidization practice relating to the desirable number of gas discharge holes per 1m of fluidized bed, and hence the flow rate per distributor in m /h is found;

c. the inside diameter of the inner pipe in mm is de termined from the formula 11.8 X flow rate, which assures a gas velocity of 30 m/s, this velocity being sufficient to entrain and thus discharge particulate material such as sand from the inner pipe;

. an available pipe size having as near as possible the calculated inside diameter is selected, the material of the pipe and wall thickness being selected having regard to service conditions; e. an outer pipe is selected with an inside diameter that gives sufficient clearance for easy assembly and disassembly, even if the pipes should have warped as a result of high temperature service. In practice, in satisfying the foregoing requirement, the other requirement of a low pressure drop in the space between the pipes is also met;

a suitable pitch for the holes is selected and whether a pair of holes or only one hole is to be used in the outer pipe at each longitudinal position is decided; from (b) and (f), the gas flow rate per hole is determined;

h. the pressure drop across the holes in the outer pipe is determined using equation 34, page 87, Fluidization Engineering, published by John Wiley (Sons, 1969. The pressure drop across the holes in the inner pipe is usually selected to be about threequarters of the pressure drop across the holes in the outer pipe;

i. from the results of (g) and (h), the hole sizes in the pipes is calculated using equations 34 to 37, pages 87 to 89 of the above reference, or equation 98, page 129, North American Combustion Handbook, first edit-ion. The calculated holes sizes in the inner and outer pipes may be so nearly equal that in practice the same size holes are used in both pipes.

The procedure outlined above was used to design the distributors in the following three practical Examples. These Examples show the specifications of gas distributors constructed in accordance with this invention which have been found to operate satisfactorily in practice.

In each Example, the holes in the inner pipe were regularly spaced along the length of the lowermost portion of the said pipe. The holes in the outer pipe were located longitudinally midway between the holes in the inner pipe and circumferentially one-eighth part of the circumference above the lowermost portion of the outer pipe, there being one hole at each longitudinal position, the said holes being placed alternately on one side and then on the other side of the lowermost portion of the outer pipe. The holes in both pipes were of the same diameter.

EXAMPLE 1 Dimensions of fluidization chamber 1m X 0.6m X 2m high Fluid bed Sand, 0.7m deep, bulk density 1400 kg/m", i.e. 600 kg of sand in bed. Temperature 850C Fluidizing gas Air, supplied through six stainless steel distributors at base of bed at a rate of 340 mlh Fuel gas burnt in the 14 m"'/h of LPG supplied through fluidized bed one stainless steel distributor located above the air distributors Air distributors Inner pipe 28 mm ID X 32 mm 0 with 36 holes, 4 mm dia at 25 mm pitch Outer pipe 38 mm ID X 42 mm 0D, with 35 holes, 4 mm dia at 25 mm pitch EXAMPLE 2 Fluid bed 3m X 1m 1m deep, having an incipient fluidization velocity of m/h per lm of bed Temperature Ambient Fluidizing gas Air supplied through 24 mild steel distributors at base of bed parallel to the 1m side of chamber at a rate four-times the incipient fluidization velocity, i.e. 55 m /h per distributor Distributors Inner pipe l2 mm ID X 18 mm OD with 35 holes, 3 mm dia at 25 mm pitch. Outer pipe 25 mm [D X 31 mm OD with 34 holes, 3 mm dia at 25 mm pitch EXAMPLE 3 Dimensions of fluidization chamber 5m X lm X2.3m high Fluid bed Sand, 1.5 m deep with incipient fluidization velocity of 30 kg/h of steam per 1m of bed Fluidizing gas Superheated steam at 35 kPa gauge pressure and 550C, supplied through 49 stainless steel distributors at base of bed Distributors Inner pipe 18.8 mm ID X 26.8 mm

OD with 18 holes, 2.4 mm dia at 50 mm pitch. Outer pipe 32.5 mm ID X 42.5

mm OD with 17 holes, 2.4 mm dia at 50 mm pitch 1 In this specification the following abbreviations have the following meanings:

m metres mm millimetres m /h cubic metres per hour m/s metres per second lm one square metre kg kilogram LPG liquid petroleum gas ID inside diameter OD outside diameter kPa kilopascals I claim:

1. Gas distributor means for use in a fluidizing vessel to fluidize particles contained in said vessel to permit operation with, if desired, intermittent fluidization, with substantial elimination of natural backflow of fluidized particles, said means comprising a pair of horizontal pipes disposed within one another and having a space between the inner pipe and the outer pipe, means for admitting fluidizing gas to the inner pipe, hole means in the inner pipe for admitting fluidizing gas from the inner pipe to the said space, hole means in the outer pipe for discharging fluidizing gas from the said space, the hole means in the outer pipe being located in the lowermost one-third ofthe circumference of said pipe and being staggered in a circumferential and/or longitudinal direction relative to the hole means in the inner pipe.

2. Gas distributor means according to claim 1, wherein said hole means are holes, and the end holes in the inner pipe are located outwardly of the end holes in the outer pipe.

3. Gas distributor means according to claim 1 wherein the hole means in the pipes are spaced in a substantially regular pattern along the length of the pipes, and are arranged symmetrically along the length of the pipes.

4. A gas distributor according to claim 1 wherein the hole means in the outer pipe are located above the lowermost portion of the pipe by a circumferential distance substantially equivalent to one-eight of the circumferen'ce of the pipe.

5. A gas distributor according to claim 1 wherein the inner pipe is disposed substantially concentrically within the outer pipe.

6. A gas distributor according to claim 1 wherein the inner pipe is disposed eccentrically within the outer pipe, the greatest distance between the adjacent surfaces of the pipes occurring substantially at the lowermost portion of these surfaces.

7. Gas distributor means according to claim 1 wherein the pressure drop of the gas in flowing through the hole means in the inner pipe is large compared with the pressure drop along the length ofthe inner pipe, and the pressure drop of the gas in flowing through the hole means in the outer pipe is large compared with the pressure drop of the gas in flowing through the space between the pipes, so that the flow of gas through the hole means in the outer pipe is substantially uniform along its length.

8. Gas distributor means according to claim 1 wherein each pair of inner and outer pipes are held in their relative positions by spacers secured to the inner pipe and spaced at intervals therearound and at intervals therealong.

9. In a fluidized bed apparatus comprising a fluidizing vessel and means for distributing a fluidizing gas in said fluidizing vessel, the improvement comprising using, as said means for distributing said gas, a plurality of pairs of horizontal pipes disposed within one another and having a space between the inner pipe and the outer pipe, means for admitting fluidizing gas to the inner pipe, first hole means in the inner pipe for admitting fluidizing gas from the inner pipe to said space, second hole means in the outer pipe for discharging fluidizing gas from said space to the fluidized bed, said second hole means being located in the lowermost one third of the circumference of said outer pipe and being staggered in a circumferential and/or longitudinal direction relative to said first hole means, whereby said fluidized bed may be operated, with, if desired, intermittant fluidization, with substantial elimination of natural backflow of fluidized particles.

10. The fluidized bed apparatus according to claim 9 wherein a series of said inner and outer pipes are connected together in parallel relationship and are arranged to extend over the area ofa fluidized bed chamber.

11. The fluidized bed apparatus as claimed in claim 9 wherein said first hole means are positioned in the lowermost portion of said inner pipe.

12. The fluidized bed apparatus as claimed in claim 11, wherein said first hole means are in the lowermost one-third of the circumference of said inner pipe.

13. The fluidized bed apparatus as claimed in claim 9, wherein the pressure drop of said fluidizing gas flowing through said first hole means is large compared to the pressure drop along the length of said-inner pipe, and the pressure drop of said fluidizing gas flowing through said second hole means is large compared to the pressure drop of the gas flowing through said space. :k 1F 

1. Gas distributor means for use in a fluidizing vessel to fluidize particles contained in said vessel to permit operation with, if desired, intermittent fluidization, with substantial elimination of natural backflow of fluidized particles, said means comprising a pair of horizontal pipes disposed within one another and having a space between the inner pipe and the outer pipe, means for admitting fluidizing gas to the inner pipe, hole means in the inner pipe for admitting fluidizing gas from the inner pipe to the said space, hole means in the outer pipe for discharging fluidizing gas from the said space, the hole means in the outer pipe being located in the lowermost one-third of the circumference of said pipe and being staggered in a circumferential and/or longitudinal direction relative to the hole means in the inner pipe.
 2. Gas distributor means according to claim 1, wherein said hole means are holes, and the end holes in the inner pipe are located outwardly of the end holes in the outer pipe.
 3. Gas distributor means according to claim 1 wherein the hole means in the pipes are spaced in a substantially regular pattern along the length of the pipes, and are arranged symmetrically along the length of the pipes.
 4. A gas distributor according to claim 1 wherein the hole means in the outer pipe are located above the lowermost portion of the pipe by a circumferential distance substantially equivalent to one-eighth of the circumference of the pipe.
 5. A gas distributor according to claim 1 wherein the inner pipe is disposed substantially concentrically within the outer pipe.
 6. A gas distributor according to claim 1 wherein the inner pipe is disposed eccentrically within the outer pipe, the greatest distance between the adjacent surfaces of the pipes occurring substantially at the lowermost portion of these surfaces.
 7. Gas distributor means according to claim 1 wherein the pressure drop of the gas in flowing through the hole means in the inner pipe is large compared with the pressure drop along the length of the inner pipe, and the pressure drop of the gas in flowing through the hole means in the outer pipe is large compared with the pressure drop of the gas in flowing through the space between the pipes, so that the flow of gas through the hole means in the outer pipe is substantially uniform along its length.
 8. Gas distributor means according to claim 1 wherein each pair of inner and outer pipes are held in their relative positions by spacers secured to the inner pipe and spaced at intervals therearound and at intervals therealong.
 9. In a fluidized bed apparatus comprising a fluidizing vessel and means for distributing a fluidizing gas in said fluidizinG vessel, the improvement comprising using, as said means for distributing said gas, a plurality of pairs of horizontal pipes disposed within one another and having a space between the inner pipe and the outer pipe, means for admitting fluidizing gas to the inner pipe, first hole means in the inner pipe for admitting fluidizing gas from the inner pipe to said space, second hole means in the outer pipe for discharging fluidizing gas from said space to the fluidized bed, said second hole means being located in the lowermost one-third of the circumference of said outer pipe and being staggered in a circumferential and/or longitudinal direction relative to said first hole means, whereby said fluidized bed may be operated, with, if desired, intermittant fluidization, with substantial elimination of natural backflow of fluidized particles.
 10. The fluidized bed apparatus according to claim 9 wherein a series of said inner and outer pipes are connected together in parallel relationship and are arranged to extend over the area of a fluidized bed chamber.
 11. The fluidized bed apparatus as claimed in claim 9 wherein said first hole means are positioned in the lowermost portion of said inner pipe.
 12. The fluidized bed apparatus as claimed in claim 11, wherein said first hole means are in the lowermost one-third of the circumference of said inner pipe.
 13. The fluidized bed apparatus as claimed in claim 9, wherein the pressure drop of said fluidizing gas flowing through said first hole means is large compared to the pressure drop along the length of said inner pipe, and the pressure drop of said fluidizing gas flowing through said second hole means is large compared to the pressure drop of the gas flowing through said space. 